Method of making rubber strips



Oct.. 5, 1937. c. BEAL 2,095,119

METHOD OF MAKING RUBBER STRIPS y Filed Maron a, 1934 Patented Oct. 5, 1937 UNITED STATES METHOD OF MAKING RUBBER STRAPS Carl L. Beal, Cuyahoga Falls, Ohio, assigner to American Anede, Inc., Akron, Ohio, a corporation of Delaware Application March 8, 1934, Serial No. 714,605

9 Claims.

This invention relates to the manufacture of elastic rubber thread, tape and similar rubber strips which are used for making stretchable fabrics, for winding golf balls, and for other purposes7 and is directed especially to a method in which the rubber strips are made by cutting a pre-formed sheet of soft rubber composition into strip form.

A method has been proposed heretofore in which a sheet of rubber is prepared and preferably although not necessarily is vulcanized to the soft rubber state in any suitable manner, and then is passed continuously through a rotary multiple disc cutter or slitter of one of several known types by means of which the sheet is slit progressively along several parallel lines to form a number of rubber strips of widths determined by the usually uniform spacing of the several rotary cutting discs. Threads or strips cut by this method have not always been entirely satisfactory, however, because they frequently exhibit feathered out edges and the gauge has not been consistently uniform, especially in very ne gauge thread 4such as that now in great demand for weaving stretchable fabrics. Such defects apparently are traceable to poor cutting caused by high cutting resistance of the rubber sheet which has not been obviated by the use, for example, of improved cutting means such as heated cutters. .The unexpected great cutting resistance of the rubber results, it is now believed, at least in part from the progressive setting up of a tough fibrous structure in localized areas of the rubber just in advance of the cutter by the creation of internal stresses produced by rubber deforming forces accompanying the cutting operation. The present invention is in part directed to a method which includes lowering the cutting resistance ofthe rubber by reducing its ability to `assume a fibrous structure when stressed, and thereby to improve the character of the cut obtainabler and to improve the quality of the cut thread. A further disadvantage of the above described method is that only a single width thread can be cut with the same set of rotary cutters, which may be said tocomprise a cutting roll, so that it is necessary to change the entire cutting roll or rolls or to change the spacing of the cutters upon the roll when it is desired to cut a different width thread. The practical objections to this feature are obvious, and the present invention is further directed to a methodwhich overcomes thisinherent disadvantage and makes possible the cutting of a wide range of thread gauges with the same cutting roll or rolls having cutting discs in a fixed spaced relation. The manner in which I secure these and other objects of the present invention will appear from the following description of a method embodying the principles of my discovery. 5

Briefly stated, the present novel method comprises preparing a sheet of soft rubber composition, preferably although not necessarily vulcanizing the rubber at least to a partial degree, subjecting the rubber sheet to a conditioning treatment designed temporarily to lower the cutting resistance of the rubber by weakening its physical strueture and reducing its ability to assume a tough fibrous structure when stressed, which conditioning treatment in'a preferred method serves also to swell the sheet a desired amount, then slitting the conditioned sheet longitudinally into a plurality of strips, and iinally restoring the out rubber to its normal physical condition. Thus, it will be seen that I cut the rubber while it is in a physically weakened condition and thereby secure a satisfactory cut edge, and also cut the sheet While it is swollen to an abnormal thickness and width so that the freshly cut strips themselves are abnormally large in cross section but upon .being restcredrto their normal state are much smaller than otherwise could have been out with the particular set or" cutters employed.

The invention as exemplied by a preferred method will be described in greater detail and with reference to the accompanying drawing in which Figs. la, and lb illustrate diagrammatically apparatus suitable for carrying out my invention.

In a preferred method, YI iirst form a sheet of unvulcanized soft rubber composition as by depositing solids from compounded liquid rubber latex, contained in a tank i, upon a rotating deposition drum ll which is partially immersed in the latex, to produce continuously a sheet of latex rubber l2 which is carried by a belt conveyor i3 through a tunnel dryer it heated in any convenient manner to a desired temperature for drying the rubber. The dried rubber sheet then is carried by a second conveyor I5 through a vulcanizer it heated in any suitable manner .to a temperature adequatetoV vulcanize the rubber at least partially and preferably completelyto an optimum soft rubber cure while it is passing throughthe vulcanizer. It is obvious that the procedure and apparatus thus far described are well known in the art and that equivalent means for preparing the vulcanized sheet, not only from latex, but from masticated solid rubber as well,

may be substitutedwithout departing from the scope of the invention. As the next step in the preferred process, Vthe rubber-sheet is directed by guide rollers I 'I, I1

itsstructure ha-s been materially weakened and Y until the sheet has been swollen by the solvent to a desired extent. weakened sheet is passed through a slitter I9 which may comprise two vsets of circularshear discs 20, 2 I mounted for'rotation upon a supporting` frame 22 with the shear discs interlacing slightly to form a multiple disc rotary shear ofthe type well known in the art. The shearing slitter cuts the sheet'longitudinally into several strips and separates thestripsinto upper and lower sets of alternate strips |2a and I2b which are carried respectively by upper andlower conveyors 23, 24 through a heated dryer and solvent recovery apparatus 25 in which the solvent is evaporated and the rubber of the strips is restored to its normal condition. Finally the finished strips are wound upon suitable reels26, 2I.

It is not possible to give definite instructions relative to the time necessary to treat the rubber with swelling agent in order to secure a desired amount of swelling, for the rate of swelling'obviously will vary'with different solvents, with variations in temperature conditions, with therthickness of the rubber sheet, with changes in the com position of the rubbeil itself, and with other like factors. Accordingly, swelling conditions which will produce a thread of a desired gauge must be determined experimentally, but as an indication of the time necessary, it has been found that a well vulcanized soft latex rubber sheet 0.01 thick when immersed in high test gasoline at ordinary room temperatures for 15 minutesv will swell about 50% in thickness so that if such a Y swollen sheet is cut with rotary knives spaced apart a Adistance corresponding to the thickness of the swollen sheet, the cut swollen thread will be 50% larger in cross section than it will be after removal of theV gasoline and restoration to its vnormal state. A well vulcanized sheet of soft rubber immersed, for example, in hightest gasocontrolled and duplicated within close limits to produce threads of uniform gauge from day to day. It is obvious that threads of different gauges may be produced merely by varying the extent to4 which the sheet'is swollenV before cutting. ,It is possible,for example, touse a single cutter with discs spaced normally to cut 100 A.gauge thread, in the production of thread varying 7 0V in gauge from 100 to 150 gauge with perfect satisfaction and without affecting the quality of the thread since the solvent treatment appears to have no permanent deleterious eifect upon the rubber. e Y y Y. In an alternative embodiment of the invention,

Thereafter Ythe swollen and I temporarily weaken the prepared soft rubber sheet before cutting by heating it to a temperature sufficiently high to reduce bering substantiallyv butrof course not sufficiently high to injure they sheet or to vulcanize it beyond a desired degree, and cut the rubber while so heated. Thus, it has been found that if a sheet is heated to a temperature of from 50 C. to 100 C., its tendency to fiber and accordingly its cutting resistance is materially and beneficially reduced. With Ysome -types of slow vulcanizing stocks which contain sub-stantially no free sulphur or which have been Ytreated to'retard vulcanization, higher temperatures may be employed in the conditioning treatment to secure increased cutting eiciency with- Y out permanent deleterious effect upon the rubber.

It is not desirable, however, to heat the vulcanized `rubber until it is actually rendered plastic or noticeablysoftened, which might injure theY rubber, since beneficial reduction in cutting resistance is obtained at lower temperatures. If desired, the sheet, while still hot from vulcanization, may be cut promptly into strip form with satisfactory results or it may be cooled and then reheatedin any convenient manner.

It is obvious thatl the methods of the .two embodiments described above may beV combined in be applied to calendered or other kmasticated rub-Y ber sheets as well. Similarly, it is not essential to the invention'hereof that the rubber be completely vulcanized, since unvulcanized or partially vulcanized sheets, or even an incompletely dried latex sheet may be treated in a similar manner,

although more care usually is required in handling the necessarily softer unvulcanized strips and it is somewhatmore difficult to control the degree of swelling. An advantageous result accrues, however, from cutting swollen or heated,Y j

unvulcanized sheet with a shearA type slitter for in such case, the cut threads are deformed during the cutting operation to produce a rounded thread in a manner similar to that described in my copending application Serial No. 693,113flled October 11, 1933, which now has matured into U. S. Patent No.,2,061,749, granted November'24, 1936.

It is apparent that the swollen or. heated rubber may be cut with any suitable devicesuch as a slitter in which a series of sharpcircular Yknives operate against a backing roll which may be grooved, or in which the knives cooperate 'with similar sharp circular knives to provide a sharp edged rotary shear, or a similar apparatus in Which the cutting discsare square faced to 'provide a'true shearing device.` Other types of cuttingior slitting devices obviously may be used.

. The cutting members of any of such devices may Vbe heated if desired Vfurther to increase their cutting efficiency. Y Y

The'term rubber has been Vemployed in va generic sense to include caoutchouc, balata,gutta percha, synthetic Vrubber andsimilar elastic gums or resins and the term latex likewise is intended to include all natural or artificial aqueous dispersions of rubber as hereinabove dned either vulcanized or unvulcanized, and whether concentrated, diluted, thickened, thinned, or otherwise preliminarily treated. The latex may contain any desirable compounding ingredients such as vulcanizing agents, age-resisters, llers, pigments, softeners, etc. commonly used in the rubber industry.

Numerous modifications and variations in the materials, apparatus, and procedure hereinabove described may be made without departing from the scope of the invention as indicated by the appended claims.

I claim:

1. The method which comprises treating rubber with a chemical swelling agent temporarily to swell the rubber and to reduce its resistance to cutting, cutting the swollen rubber into desired form, and restoring the cut rubber to its normal unswollen condition.

2. 'I'he method which comprises treating rubber with an organic swelling agent to swell the rubber and to reduce its resistance to cutting, cutting the swollen rubber, and restoring the out rubber to its normal unswollen condition.

3. The method which comprises preparing a sheet of soft rubber, immersing the sheet in a liquid swelling agent until it is swollen to a substantial extent, cutting the swollen sheet into strip form, and removing swelling agent from the out strips to restore the rubber thereof to its normal unswollen condition.

4. The method which comprises preparingV a sheet of soft rubber, treating the rubber with an organic swelling agent to swell the rubber and to reduce its resistance to cutting, cutting the swollen rubber sheet simultaneously along a plurality of parallel lines to produce a plurality of rubber strips, and removing swelling agent froml the 4cut strips to restore the rubber thereof to its normal unswollen condition.

5. The method which comprises preparing a sheet of unvulcanized rubber composition, vulcanizing the rubber, treating the vulcanized rubber sheet with a liquid swelling agent until the sheet is swollen to a substantial extent, cutting the swollen sheet into strip form, and removing swelling agent from the cut strips to restore the rubber thereof to its normal unswollen condition.

6. The method which comprises preparing a sheet of unvulcanized rubber composition, treat'- ing a substantial portion of the unvulcanized rubber sheet with a swelling agent temporarily to weaken it and to reduce its resistance both to cutting and to deformation, thereafter passing the treated portion of the sheet through a rotary multiple disc shear to cut the rubber and to deform' the rubber as it is cut to produce rounded rubber strips, and restoring the rubber of the cut strips to its normal physical condition.

7. The method which comprises forming from liquid rubber latex a coherent sheet of soft latex rubber composition having a high resistance to cutting, temporarily weakening the rubber by treatment with a chemical swelling agent to reduce its resistance to cutting, cutting the temporarily weakened rubber into desired form, and restoring the cut rubber to its normal condition.

8. 'Ihe method which comprises preparing an unvulcanized but vulcanizable rubber composition, at least partially vulcanizing the rubber, swelling the at least partially vulcanized rubber by treatm-ent with a liquid swelling agent, `cutting the swollen rubber into desired form, and restoring the cut rubber to its normal unswollen con-V dition.

9. The method Which comprises preparing an unvulcanized but vulcanizable rubber composition, vulcanizing the rubber to an optimum softvulcanized rubber state, swelling the vulcanized rubber by treatment with a liquid swelling agent, cutting the swollen rubber into desired form, and restoring the cut rubber to its normal unswollen condition.

CARL L. BEAL. 

